LCD Power Consumption Is In Your Hands! Display Power Consumption: CRTs Versus TFT-LCDs : New LCD flat panel displays are constantly reaching record lows in power …An increasing number of flat panel displays are based on LED backlighting, and their manufacturers aren't shy about promoting the technology's benefits to power …This got me thinking about power consumption, and then about LCD … of LCDs when theyre still twice as much as CRTs … decrease in heat generated by the LCD monitors versus …

Post author: kashinomi

An increasing number of flat panel displays are based on LED backlighting, and their manufacturers aren’t shy about promoting the technology’s benefits to power consumption. We checked the claims to see if the promised savings are worth emphasizing.

New LCD flat panel displays are constantly reaching record lows in power consumption: 50 W, 40 W, and even 30 W are sometimes achieved in displays as large as 24” these days. The most important variable in display power savings is the backlight technology. Today, we have fluorescent lighting transitioning to light-emitting diodes (LEDs). We grabbed all of our test lab’s LCD monitors and two old CRTs, pitting them against each other in a power consumption shootout.
Display Power Becoming Important
As of late, we’ve written a lot about power consumption on the system side, where usage is most noticeable. Processors and graphics cards were particularly blatant consumers a few years ago. Nowadays, the trend (especially in Europe) is mostly toward more environmentally-friendly components.
Green computing has forced even the largest corporations to rethink and refocus. We have low-power processors, motherboards, memory modules, hard drives, and even high-efficiency power supplies. Many things have changed, but you still need to look at every product individually to decide whether or not it’s truly efficient.
Interestingly, displays were largely neglected in this “green refresh.” Part of the reason was that, ever since LCDs displaced CRT displays, the typical PC utilizes more power than its attached monitor. However, this is changing rapidly. Enthusiast PCs, gaming systems, and workstations still often consume more than 100 W at idle and much more under load. But the majority of PCs sold are business and mainstream systems, and the average power consumption in this group is dropping fast thanks to aggressive optimization.
Display Power Higher Than System Power?
As a result, mainstream PCs that don’t sport discrete graphics and multi-core processors consume reasonable amounts of power. In the article Build a 25 W Performance PC Using Core i5, we proved that a system with above-average performance does not have to draw more than 25 W at idle. Since most 20″ or higher flat panels consume 30 or 40 W, it’s likely that your display will chew up more power than your nettop or mainstream system.
We decided to run a little analysis on the following displays from our test lab:
CRT:
* Iiyama Vision Master Pro 454 (19”, 2003)
* Sony Multiscan G420 (19”, 2002)
LCDs:
* 19” Benq FP937S (2005)
* 20” Samsung SyncMaster 204B (2006)
* 24” Samsung SyncMaster 245B Plus (2008)
* 19” Philips 190BW9 (2009)
* 22” Acer P225HQL (2010)
There’s no point in stretching out a CRT discussion, since these are largely obsolete. Suffice it to say that cathode ray tube designs use an electron gun that draws images onto a fluorescent screen, line by line. At refresh rate of at least 75 Hz is desirable for a flicker-free image; 85 Hz or more is better. CRTs are housed in glass envelopes, making them physically deep, heavy, fragile, and susceptible to magnetic interference. They’re also environmentally unfriendly, owing to various toxic coatings. High-frequency noise, possible implosion (it’s a vacuum tube), and some radiation also don’t help curry favor when comparing to LCD technology. CRTs do have some advantages, but they are overshadowed nowadays.
Unlike CRT displays, every LCD has a native resolution at which it should operate for optimal image quality. Setting a native 1920×1080 display to only 1600×900 results in blurry images, as the output resolution has to be converted to the physical resolution. For best quality results, use digital connections to LCDs, such as DVI, HDMI, and DisplayPort. Avoid the old, analog 15-pin D-Sub connections that converted digital output into an analog signal for transmission, then re-digitize it for display on your LCD monitor. Such conversions always result in image quality loss that can be avoided by a digital link.
Most modern LCD monitors are based on active matrix thin-film transistor (TFT) technology. These displays are based on a TFT array substrate containing transistors, capacitors, wiring, and pixel electrodes, which serve to apply voltage between the TFT substrate and the color filter substrate, which contains red, green, and blue sub-pixels. The two glass substrates are kept apart by spacers and cells filled with liquid crystal material. The outer faces of the TFT panel are equipped with polarizing sheets. Finally, data lines attach to LCD driver chips. Each pixel can be addressed separately in this matrix through the bonding pads at the end of each row and column, as if the monitor were lighting up pixels by playing Battleship.
LCD Panel Types
There are significant differences in performance and characteristics between one LCD display and the next. As with most technologies, you can generally assume that newer products are superior (of course, this isn’t always the case). Details like response time and input lag (the time required to change a pixel’s color and to have an input signal change the display, respectively), viewing angle, brightness, and contrast improve from one generation to the next.
Twisted nematic (TN) panels are the most widespread TFT type, offering response times of only a few milliseconds (though response time varies between different color transitions). Contrast, viewing angle, and color reproduction remain issues, especially with low-cost TN devices. Color reproduction can be problematic for image processing or other professional applications, given that each color is typically represented by only six bits, resulting in 18 bits as opposed to the 24-bit color necessary for 16.7 million true colors.
In-plane switching (IPS) panels have the liquid crystals in parallel to the panel, not perpendicular to it. Viewing angles are much wider, and light scatters much less within the matrix, which is why color reproduction can be more precise. Initially, this precision came at the expense of response time. Advanced Super-IPS (AS-IPS) provides an improved contrast ratio, and Horizontal-IPS (H-IPS) works on professional LCDs for a more natural white color. Enhanced-IPS (E-IPS) is more advanced still, bringing response time back to only a few milliseconds, but it’s much more expensive than a TN panel.
Multi-domain vertical alignment (MVA) panels are a compromise between TN and IPS. Colors don’t change as much if you move away from a perfect 90° relative to the monitor’s screen plane. Color reproduction and response time are good, too. Patterned vertical alignment (PVA) is a similar technology with higher contrast. S-PVA is considered the most advanced technology of the group, utilizing more than eight bits per color, showing the deepest blacks, and offering the quickest response times.
Recently, conventional fluorescent backlights are being replaced by white LEDs. These typically last longer and consume less power, which is the main motivation for our analysis. Do LEDs really make that much of a difference? Let’s find out.
These are our tested LCDs in chronological order.
19” Benq FP937S (2005)
Today, a 1280×1024, 19″ unit like the FP937S is no longer special, and the display’s color reproduction is pathetic compared to newer products. A 12 ms response time, 250 cd/m², and 500:1 contrast ratio no longer impress, either. Still, if you don’t compare it directly to newer products, this relic works well enough. Power consumption is amazingly low at a maximum of 32 W, although you pay a price in having no digital connection ports.
20” Samsung SyncMaster 204B (2006)
This 20” TN panel is still decent, and was one of the first more affordable displays in 2006. It debuted under $400 and offered solid value. Compared to the newer 245B Plus (see below), the 204B outputs a more “yellow” white, but it also has much lower power consumption, staying below 35 W. This is very close to Samsung’s 36 W specification.
24” Samsung SyncMaster 245B Plus (2008)
The 245B Plus was originally priced just below $400. Its colors are colder than those on the 204B, and we don’t trust the 245B Plus’s color reproduction much. But the display turned out to be a good fit for office and multimedia applications, thanks to its 16:10 image ratio. We like that its height can be adjusted—something many display manufacturers quietly drop when they try to shave cost from mainstream products.
19” Philips 190BW9 (2009)
This 19”, 16:9 display isn’t particularly special in terms of display quality. But its 1680×1050 resolution is excellent for office applications. The screen has DVI and D-Sub inputs (budget hardware doesn’t always offer both), speakers, height adjustment, a USB 2.0 hub, and a VESA wall mount. Last year, the 190BW9 solf for under $150.
22” Acer P225HQL (2010)
This is the only LCD display in our test lab with an LED backlight. The P225HQL is a 22” device with HD resolution (1920×1080) and a 16:9 aspect ratio. You can’t adjust height, and the glossy black housing demands regular cleaning. In addition, the image is somewhat cold and bluish. But again, it’s fine for our test lab’s purposes.
Iiyama Vision Master Pro 454 (19”, 2003)
We reviewed this monitor in 2002. It was an upper-mainstream 19” unit enabling impressive resolutions and supporting high frequencies of 115 kHz on its DiamondTron tube. This was enough to run up to 1920×1440 at 77 Hz. We used a 1600×1200 resolution at 85 Hz for our testing. Iiyama’s specifications say that it consumes up to 145 W. We didn’t get that high. At 100% brightness, it pulled just over 100 W.
Sony Multiscan G420 (19”, 2002)
Test Environment
System Hardware
Hardware
Details
Motherboard (Socket LGA1156)
Zotac H55 ITX-WiFi (Rev. 1.0), Chipset: Intel H55, BIOS: 1.3
CPU Intel
Intel Core i3-530 (32 nm, 2.93 GHz, 4 x 256 KB L2 and 4 MB L3 Cache, TDP: 73 W)
Display I (CRT)Iiyama Vision Master Pro 454, 1920×1440, 19″, 4:3, 115 Hz
Display II (CRT)Sony CPD-G420, 1920×1440, 19″, 4:3, 110 Hz
Display I (TFT)Philips 190BW9, 1680×1050, 16:9, 19″, TN panel
Display II (TFT)Samsung SyncMaster 245B Plus, 1920×1200, 16:10, 24″, TN panel
Display III (TFT)Samsung SyncMaster 204B, 1600×1200, 4:3, 20″, TN panel
Display IV (TFT)Acer P225HQL, 1920×1080, 22″, 16:9, LED Backlight, TN panel
Display V (TFT)
BenQ FP937S, 1280×1024, 4:3, 19″, TN panel
RAM
2 x 2 GB DDR3-1333 (OCZ3G2000LV4GK 8-8-8-24), dual-channel mode
HDD
Seagate Barracuda 7200.11, 500 GB (ST3500320AS),7200 RPM, SATA 3Gb/s, 32 MB Cache
Power Supply
Enermax Pro 82+, EPR425AWT, 425 W
System Software & Drivers
Operating System
Windows 7 Ultimate x64, Updated on 2010-03-03
Drivers and Settings
Intel Chipset Drivers
Chipset Installation Utility Ver. 9.1.1.1025
Intel Storage Drivers
Matrix Storage Drivers Ver. 8.​9.​0.​1023
Intel GraphicsIntel Graphics Media Accelerator 15.17
All LCD-based displays operate at their native resolutions and 60 Hz. The CRT display runs at 1600×1200, 85 Hz. Brightness was always set to 100%, which may not be realistic, but it represents the worst-case scenario. The last test results demonstrate power consumption at decreased brightness.
Running at 100% brightness represents a worst-case scenario for power consumption. The results match our test with Microsoft Word and a blank page.
Switching brightness to 50% makes a significant difference, as the displays reduce their power consumption as follows:
* Acer 22”: 18 W to 13 W (-28%)
* Philips 19”: 31 W to 21 W (-32%)
* BenQ 19”: 32 W to 24 W (-25%)
* Samsung 20”: 34 W to 25 W (-26%)
* Samsung 24”: 66 W to 44 W (-33%)
* Iiyama 19” CRT: 102 W to 98 W (-4%)
* Sony 19” CRT: 111 to 103 W (-7%)

Finally, the reduction to only 10% display brightness dramatically reduces power consumption with a white screen to as little as 9 W on the 22” Acer display, 12 to 21 W on the 19”/20” displays, and 26 W on the 24” Samsung. The only monitors showing little impact are the CRTs.
We can confirm that the TFT display with LED backlighting is indeed lowest on overall power consumption. Of course, we’re only talking about the displays in our lab here, not generalizing about the entire display market. With that said, other LED-lit displays are likely lower on power consumption than models with fluorescent lighting. The overall image is colder and may appear bluish, but this can be adjusted in the monitor settings.
We can also confirm that CRTs will require at least twice the power of an LCD display. You could operate three large, modern LCDs with the power consumed by one 19” CRT, and this ratio will probably become 4:1 very soon. If you care about energy savings, you should dispose of your old CRT monitor once you find a good deal on a decent LCD. Even if power isn’t your primary concern, consider that LCDs don’t get as hot as CRT monitors for the very same reasons. We found that it’s hardly possible to reduce power consumption by decreasing monitor brightness, but LCD power draw varied significantly as brightness changed. Specifically:
* We could reduce power consumption by up to 65% just by reducing brightness.
* Newer displays will show more significant power savings with reduced brightness.
* Larger displays need more background light, but operating power can still be reduced.
* Even older displays require less power if brightness is reduced.
A 20% brightness reduction might not impact your visual experience very much, but it could reduce the power consumption of your display to a larger extent than typical efforts to reduce system power consumption by using low-power hardware, such as an efficient power supply, green drives, or SSDs.
We recommend checking your display brightness setting. Working with documents and spreadsheets typically doesn’t require more than 250 cd/m², and many people habitually set their monitors with too much brightness. You couldn’t ask for easier (free) power savings. Those looking for a new display should target high contrast ratios, since this allows for decreasing the brightness. Of course, be sure to account for personal preferences, environmental lighting, hardware, and your applications when choosing brightness settings. Power savings shouldn’t have to result in eye strain.

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